Help!!! Very low oil pressure on '02 E66/745Li w/110K mi

I reach out for help to those of you most knowledgeable about the N62 engines. Several weeks ago I began having a low oil pressure problem -- measured at the oil pressure switch bore on the passenger side of the engine. Since then I removed the oil pressure switch and replaced it with an analog gauge, which confirms a pressure of up to ~10 psi when the engine is cold, dropping to 1-2 psi when nearing normal operating temperature.

I am running the standard full synthetic 5W-30 that the dealerships, shops, and many articles approve for these engines at all ages. Going back and forth between my father and I (side note: this is my car, not his), we decided to replace the oil pump -- which on this engine also contains check valve / pressure relief valve and filter assembly. My heart began to sink when I pulled the old pump apart and didn't see any sign of wear or a single thing out of place; it was pristine. This past Sunday I got the car all back together, new oil [again] and all, just to find that the problem is still there. Nothing at all has changed.

My questions to you who are reading this: are there any common causes of this issue on these engines? How would you go about finding the location of the pressure leak if this was your car?

Am I looking at a blockage (note: all oil filters have been extremely clean)? A backed-out bolt in the valvetrain somewhere? Cracked block? Blown head gasket? Bearings?

If the pump appears to be okay, the next step is to measure the rod and main bearing clearances. Check the clearances on the main bearing closest to the pump (this has the greatest effect on pressure) and clearances on the furthest rod bearing (this will show the greatest wear).

If the bearings are worn, they need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals need attention, the crank will also have to be reground or replaced.

BMW Oil Pressure Diagnostic Tips :
A good place to start your diagnosis of a low pressure condition is at the dipstick. Check the oil to see that it's at the proper level (not low nor overfilled). If low, the engine may be burning or leaking oil. Adding oil may temporarily remedy the low pressure condition, but unless the level is properly maintained, the problem may recur.

If the engine is leaking oil, try new gaskets or seals to fix the leak. If the engine is burning oil, the valve guides and seals are most likely worn, but the rings and cylinders might be bad, too. A wet compression test and/or leakdown test will tell you if it's the valve guides or rings and cylinders that are worn.

The least expensive fix in the case of worn guides is to install new valve guide seals (if possible) without pulling the head.

The best fix is to pull the heads and have the guides lined, knurled, replaced or reamed for oversized valve stems. Worn rings and cylinders would call for a complete overhaul.

Also note the condition of the oil and make sure it's the correct viscosity for your BMW and climate.

Heavier viscosities, such as 20W-50, straight 30W or 40W, may help maintain good pressure in hot weather but are too thick for cold weather driving and may cause start-up lubrication problems - especially in overhead cam engines.

Light viscosities, on the other hand, such as straight 10W or 5W-20, may improve cold weather starting and lubrication but may be too thin in hot weather driving to maintain good pressure.

That's why most car and OE parts manufacturers recommend 5W-30 in modern engines for year-round driving.

If the level is okay, the next thing to check would probably be the pressure sending unit. Disconnect the unit and check the warning lamp or gauge reading.

If the warning light remains on with the sending unit disconnected, there's probably a short to ground in the warning lamp circuit. Likewise, if there's no change in a gauge reading, the problem is in the instrumentation, not the engine.

Bad sending units are quite common, so many mechanics replace the unit without checking anything else to see if that cures the problem. This approach might save time, but it's risky because unless you measure pressure directly with a gauge attached to the engine, you have no way of knowing if pressure is within specifications or not.

Most warning lamps won't come on until pressure is dangerously low (less than four or five pounds). So don't assume the absence of a warning lamp means pressure is okay, especially if the engine is making any valve or bearing noise.

If a check of pressure reveals unusually low readings, check the filter. It's possible the filter might be plugged with gunk. Replace the filter and see if that makes a difference.

The next step is to drop the oil pan and check the oil pump pickup screen. If the screen is clogged with debris, you've found the problem. Also, check to see that the pickup tube is properly mounted and positioned, is firmly attached to the pump (no leaks) and is not obstructed.

If the pump is mounted inside the crankcase, the next step might be to remove and inspect the pump. Open the pump cover and measure clearances. Also, check for scoring or other damage. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, replacement is your only option.

If the pump appears to be okay, the next step is to measure the rod and main bearing clearances. Check the clearances on the main bearing closest to the pump (this has the greatest effect on pressure) and clearances on the furthest rod bearing (this will show the greatest wear).

If the bearings are worn, they need to be replaced. But before you do so, carefully inspect and measure the crankshaft journals to check for wear, scoring, out-of-round and taper. If the journals need attention, the crank will also have to be reground or replaced.

Other diagnostic checks might include camshaft end play and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters.

Remember, excessive clearances or leaks anywhere in the engine's oil supply system can contribute to low pressure.

Once you've identified and repaired discovered problems, your final check is to start the engine and make sure pressure is within BMW specifications. Use a mechanical pressure gauge and don't rely on the dash gauge or the warning light to verify that the repairs you've made have eliminated your problem. from autohauz.com

If you mean the crankshaft bearing, I believe you will have to drop the transmission, but not necessarily the engine. I need more specific info on exactly what you mean.

If you go to REALOEM.com you will be able to enter your VIN # and retrieve detailed diagrams of your car. FInd the exact parts you wish to check on, and then google for some DIY's or other info. If you get detailed enough info, I can try to help you more.

Also - Sometimes oil pressure is affected by very small details -- Failed o-rings on the dipstick tube, defective oil filters, etc. This is the kind of thing that a friendly BMW mechanic could troubleshoot for you, and at least point you int he right direction as to potential causes as well as potential solutions.

For instance, on E36 3-ers...BMW literature recommends lifting the whole engine up to create enough clearance to remove the oil pan. If you talk to someone who actually does this repair, they will tell you to brace the engine, and lift the transmission 3mm to create the clearance necessary. I don't know the E66 as well as I know the E36, so I am not an expert - but I bet an expert will be like, "Oh...low oil pressure? 745? That is because the sump for the driver's side bank has a misaligned feed tube (hypothetical)."

Thanks a bunch for the replies. You are correct; I was referring to any and all bearings along the crank -- though I'm praying that I don't have to see that side of the engine again. I'm hoping for maybe a blockage, backed-out bolt, or bad seal.

That being said, I DO have some modifications to the TIS procedure for replacing the oil pump if anyone needs to replace a seal down there. Words of wisdom to anyone reading this: when the service techs at your local dealership/shop say "the oil pumps never go on these things", they are right. Period. If you think the oil pump on your '02-'04 745i/745Li crapped out, you're wrong -- take it from someone who just dropped $600 for no good reason on a new one. If I get around to posting some pictures of my old one, you'll see why these things will practically never wear out (well past 100K miles) -- it's just in the design, though I have read about check valve springs breaking (though not mine, unfortunately).

I digress. To replace the oil pump or take down the front axle support is really not THAT difficult, just a little tedious. And no, you don't need their several-thousand-dollar front axle support frame / "take-up fixture" shown in TIS, nor any other tools you can't make yourself in 10 minutes. For anyone reading this, I offer some words to the wise and a quick run-down of the procedure: keep track of your bolts, get a long piece of steel + drill press + file to make your water pump pulley-holder tool to help take the fan off (look at the "special tool" for this in TIS (not rocket science to make one of these, and it will undoubtedly come in handy if you frequently lay hands on your own cars like me), put the car up on sturdy jack stands (just jack the car up from the plastic pad on the middle of the axle support - though BLOCK THE BACK TIRES FIRST!!!), take the front wheels off (trust me, you'll need the room), take the fan and fan shroud out, take out the brake vents (coming from the front air dam - adds to elbow room), take off the belts, take off the reinforcement plate covering the lower sump/oil pan, use the driver's seatbelt wrapped around the steering wheel to keep the steering wheel straight (IMPORTANT), unbolt and yank out (figuratively) the steering column's universal joint from the steering gear and column (located immediately toward the engine from the top of the driver's side brake rotor), unbolt the A/C belt tensioner, unbolt the power steering pump and pull it forward/out a little (make sure to hang it from a pulley with a wire coat hanger), unbolt the motor mounts from the front axle support frame, lift the engine the recommended 10mm (which is basically just enough to ensure that all its weight is off the subframe), jack up the axle support frame with enough force to hold it in place (nothing excessive, just hold it up) using a jack under the plastic pad again, there are some some plastic clips that keep a few metal lines at the rear passenger side of the subframe bolted to it - you'll want to unbolt these (or you'll end up breaking the plastic clips when you lower the subframe like I did), pull out the 6 front axle support frame bolts, get out your tap / die set and thread two roughly 10-inch metal dowels with about an inch of the same threading as the subframe bolts (I forget - I think maybe M12x1.5 ?), put your fancy newly-threaded dowels in the "middle" subframe holes (the ones closest to where the motor mounts bolt in), lower the jack on the subframe until you have about 3"-4" between the frame of the car and the front axle support subframe (this is about the right amount to get the upper sump / oil pump dropped down and out of the way of the oil pump gear and chain), ... and voila, you can drop the upper sump and oil pump. Disclaimer: again, if you think your 745i/745Li's oil pump is shot, you are wrong. Believe me. Regardless, as I said earlier, this is tedious and requires a little patience, but not at all difficult, and you just saved yourself paying for about 16 hours at $116/hr.

Thanks a bunch for the replies. You are correct; I was referring to any and all bearings along the crank -- though I'm praying that I don't have to see that side of the engine again. I'm hoping for maybe a blockage, backed-out bolt, or bad seal.

That being said, I DO have some modifications to the TIS procedure for replacing the oil pump if anyone needs to replace a seal down there. Words of wisdom to anyone reading this: when the service techs at your local dealership/shop say "the oil pumps never go on these things", they are right. Period. If you think the oil pump on your '02-'04 745i/745Li crapped out, you're wrong -- take it from someone who just dropped $600 for no good reason on a new one. If I get around to posting some pictures of my old one, you'll see why these things will practically never wear out (well past 100K miles) -- it's just in the design, though I have read about check valve springs breaking (though not mine, unfortunately).

I digress. To replace the oil pump or take down the front axle support is really not THAT difficult, just a little tedious. And no, you don't need their several-thousand-dollar front axle support frame / "take-up fixture" shown in TIS, nor any other tools you can't make yourself in 10 minutes. For anyone reading this, I offer some words to the wise and a quick run-down of the procedure: keep track of your bolts, get a long piece of steel + drill press + file to make your water pump pulley-holder tool to help take the fan off (look at the "special tool" for this in TIS (not rocket science to make one of these, and it will undoubtedly come in handy if you frequently lay hands on your own cars like me), put the car up on sturdy jack stands (just jack the car up from the plastic pad on the middle of the axle support - though BLOCK THE BACK TIRES FIRST!!!), take the front wheels off (trust me, you'll need the room), take the fan and fan shroud out, take out the brake vents (coming from the front air dam - adds to elbow room), take off the belts, take off the reinforcement plate covering the lower sump/oil pan, use the driver's seatbelt wrapped around the steering wheel to keep the steering wheel straight (IMPORTANT), unbolt and yank out (figuratively) the steering column's universal joint from the steering gear and column (located immediately toward the engine from the top of the driver's side brake rotor), unbolt the A/C belt tensioner, unbolt the power steering pump and pull it forward/out a little (make sure to hang it from a pulley with a wire coat hanger), unbolt the motor mounts from the front axle support frame, lift the engine the recommended 10mm (which is basically just enough to ensure that all its weight is off the subframe), jack up the axle support frame with enough force to hold it in place (nothing excessive, just hold it up) using a jack under the plastic pad again, there are some some plastic clips that keep a few metal lines at the rear passenger side of the subframe bolted to it - you'll want to unbolt these (or you'll end up breaking the plastic clips when you lower the subframe like I did), pull out the 6 front axle support frame bolts, get out your tap / die set and thread two roughly 10-inch metal dowels with about an inch of the same threading as the subframe bolts (I forget - I think maybe M12x1.5 ?), put your fancy newly-threaded dowels in the "middle" subframe holes (the ones closest to where the motor mounts bolt in), lower the jack on the subframe until you have about 3"-4" between the frame of the car and the front axle support subframe (this is about the right amount to get the upper sump / oil pump dropped down and out of the way of the oil pump gear and chain), ... and voila, you can drop the upper sump and oil pump. Disclaimer: again, if you think your 745i/745Li's oil pump is shot, you are wrong. Believe me. Regardless, as I said earlier, this is tedious and requires a little patience, but not at all difficult, and you just saved yourself paying for about 16 hours at $116/hr.

Sounds like a good DIY. If it had pictures it would be as good as a Bentley!

I have not yet entirely eliminated the possibility that the low pressure condition is due to worn crank bearings (engine noises do not indicate such a condition, and I really don't feel like taking the oil pump down again to pressurize if I don't have to). Currently I am pulling off the valve covers to check for odd leakage. I connected 20-60 psi of air to the [previous] oil pressure switch location and found air/oil spitting out from what appears to be a bore related to the intake and exhaust VANOS solenoids (part 7) (the ones that poke out the front of the timing case) as well as two of the HVAs, all on the passenger / 1-4 cyl bank side.

Update: FINALLY found the issue -- chunk of hard plastic stuck in the check valve leading to the oil pressure switch and another between the oil pump and check valves. I got the second piece of plastic out by taking the oil pump BACK down AGAIN and sticking a vacuum cleaner on the main pressure bore going into the block from the oil pump. Will update this with more info and pictures later (I have to crop and narrow down from somewhere in the range of 150 pictures).

However, I have a new problem: the car will now not start. Fyi, the battery died while the days working on the car flew by. Recharged battery, car is now back together, cranks over happy as can be, but it won't kick over and actually start. Any immediate thoughts? Thanks in advance!